It is known that animals such as poultry are very susceptible to extremes in temperature. A substantial proportion of a poultry farmer's flock may die if the temperature inside the poultry shed becomes too hot or too cold. Even with minor variations in temperature, egg production may fall significantly. The preferred temperature is from 19.degree. to 30.degree. celsius. Variations above or below 19.degree. to 30.degree. can reduce egg production effeciency from 80% to 50% for example. Even minor variations above 26.degree. or below 20.degree. can reduce efficiency by 5%. (100% egg production efficiency is taken to be production of one egg per hen per day). It has also been found that average egg production is higher during spring and autumn when the temperature does not vary as much as during summer and winter.
As most poultry sheds are of sheet iron construction, the inside of the shed is not effectively insulated from the outside environment and the inside temperature will vary significantly. In fact, the temperature inside the sheet iron poultry shed during summer days can be a great deal higher than the outside air temperature. A further factor which affects the temperature inside the poultry shed is the body heat produced by the chickens. In a typical chicken shed, the cages may be stacked three high across the width of the shed, and there may be up to 300 chickens per meter along the length of the shed. As each chicken produces approximately 31 BTU per hour, the body heat produced by the chickens is of the order of 10,000 BTU per hour per meter of length of chicken shed. If adequate cooling is not provided, the effect of body heat can result in the death of a high proportion of the chickens.
It has been known to provide air conditioning and cooling systems during summer and hot days, as well as heating systems during winter and cold nights. Such cooling and heating systems are very expensive however, due to the large space to be cooled or heated, as the case may be.